Polypyridobisimidazole polymer is a rigid rod polymer. Fiber made from this polymer, one polymer composition of which is referred to as PIPD and known as the polymer used to make M5® fiber, is known to be useful in both cut and flame resistant protective apparel. See, for example, PCT Application WO199902169 and WO2005002376. Fibers made from rigid-rod polymers having strong hydrogen bonds between polymer chains, e.g., polypyridobisimidazoles, have been described in U.S. Pat. No. 5,674,969 to Sikkema et al. An example of a polypyridobisimidazole includes poly(1,4-(2,5-dihydroxy)phenylene-2,6-pyrido[2,3-d:5,6-d′]bisimidazole), which can be prepared by the condensation polymerization of tetraaminopyridine and 2,5-dihydroxyterephthalic acid in polyphosphoric acid. Sikkema describes that in making one- or two-dimensional objects, such as fibers, films, tapes, and the like, it is desired that polypyridobisimidazoles have a high molecular weight corresponding to a relative viscosity (“Vrel” or “ηrel”) of at least about 3.5, preferably at least about 5, and more particularly equal to or higher than about 10, when measured at a polymer concentration of 0.25 g/dl in methane sulfonic acid at 25° C. Sikkema also discloses that good fiber spinning results are obtained with poly[pyridobisimidazole-2,6-diyl(2,5-dihydroxy-p-phenylene)] having relative viscosities greater than about 12, and that relative viscosities of over 50 (corresponding to inherent viscosities greater than about 15.6 dl/g) can be achieved.
The use of polybenzobisoxiazole (PBO) fiber and polybisimidazole in cut resistant, spike resistant or ballistic resistant fiber has been reported. See, generally, U.S. Patent Application No. 2005/0003727, PCT Patent Application Nos. WO2005002376, WO2004018754, and WO2005/001373.
U.S. Patent Application No.2003/0228812 discloses the use of polybenzimidazole (PBI) and PBO fibers in protective apparel. PCT Patent Application No. WO2004023909 discloses the use of polybenzimidazole and poly(paraphephenylene benzobisaxazole) fibers and filaments in fabrics. A number of patent and patent applications report blends of aramid fiber with PBO fiber. See U.S. Patent Application Nos. 2005/0065146, 2003/0228821, and 2003/0203690, and U.S. Pat. Nos. 5,233,821, 6,624,096, and 6,914,022. In addition, polybenzimidazole fiber is currently blended with aramids in commercially available fabrics. The aforementioned polybenzimidazole, however, is a polybibenzimidazole polymer and is not a rigid rod polymer. Thus, the fiber has low strength compared to a rigid rod polymer.
Thermal and flame retardant protective apparel has been used by firefighters, emergency response personnel, members of the military and racing personnel to save lives and reduce injury due to fires and other thermal events. While polybenzobisoxazole fiber has high strength and excellent fire resistant properties, fabrics and garments made from such fibers are highly susceptible to damage from ultraviolet (UV) light, which results in severe loss of fiber strength and consequently compromises fabric and garment durability. There is also a desire to incorporate polypyridobisimidazole fibers into fabrics and garments to take advantage of this fiber's superior flame resistant properties and high strength. Thus, there is a need for a fabric containing both polybenzobisoxazole and polypyridobisimidazole fiber that is tolerant of UV light and therefore is more durable as an outer shell fabric of a garment while providing excellent fire protection properties.